//rem自动计算
(function (doc, win) {
  var docEl = doc.documentElement,
    resizeEvt = "orientationchange" in window ? "orientationchange" : "resize",
    recalc = function () {
      // 获取设备的宽度
      var clientWidth = docEl.clientWidth;
      if (!clientWidth) return;
      // html的fontsize = 设备的宽度 * 100  / 750
      docEl.style.fontSize = (100 * clientWidth) / 750 + "px";
    };

  if (!doc.addEventListener) return;
  win.addEventListener(resizeEvt, recalc, false);
  doc.addEventListener("DOMContentLoaded", recalc, false);
})(document, window);
